94 Pickup: Speedometer & Heater Controller Problems

[red.cherokee]

Hello all. I've searched for an answer but did not find it. I don't know if these two problems are related or not, can you help?

Problem #1 is the speedometer was working fine, then one day while driving it would go to zero and bounce back to normal. Gradually got worse. Would be at zero until I had driven for 20 minutes and then it would start working. Now it has quit all together. After the speedometer has not worked for about 5 miles, the Check Enging light comes on, sometimes the brake light comes on?

A couple days later the heater/AC controller messed up. The temperature indicator arrow has gone away, and the heater startsed blowing hot air. When I try to adjust the temp, all of the temp indicator arrows start flashing, and unable to control the heat. I can select weather the air blows out the vent or on the floor, and I can turn the fan up higher, but can't turn it off.

I don't know if these two problems are related or just happened at about the same time? Can you help please. Thank you.

[mr_mushroom]

at first glance, they seem unrelated.
i can't help you with the climate control problem, i don't know how the electronic ones work.
the speedometer problem is most likely due to the speed sensor coming loose either at the transmission tailshaft or at the back of the speedometer itself.
you have OBD-II so that tells me that the speedometer problem is transmission related. because your light is coming on, mostly. you'll want to pull the code to see if it's related, however. if the computer isn't getting a signal from the speedometer sender, it will trip a check engine light.
check up on it and let us know.

[red.cherokee]

That makes sense that the problem is at the transmission end, causing the Service Engine light to come on. I read on here that I need to ground contact A and B to get the code, is that correct? When I ground them together, do I only touch them for a second, or do I need to keep them contacted while the code is flashing? thanks for your response.

[2000CAYukon]

Originally Posted by red.cherokee

That makes sense that the problem is at the transmission end, causing the Service Engine light to come on. I read on here that I need to ground contact A and B to get the code, is that correct? When I ground them together, do I only touch them for a second, or do I need to keep them contacted while the code is flashing? thanks for your response.

You need to leave them contacted while you read the code.

See www.troublecodes.net/GM

//2000CAYukon

[red.cherokee]

Thanks for the link.

[yazou]

Do you have find your problem (speedometer & heater problem) ,because i got the same problem with mine before (94 chevy truck 4x4) and now its fix.

[jocat54]

Originally Posted by mr_mushroom

at first glance, they seem unrelated.
i can't help you with the climate control problem, i don't know how the electronic ones work.
the speedometer problem is most likely due to the speed sensor coming loose either at the transmission tailshaft or at the back of the speedometer itself.
you have OBD-II so that tells me that the speedometer problem is transmission related. because your light is coming on, mostly. you'll want to pull the code to see if it's related, however. if the computer isn't getting a signal from the speedometer sender, it will trip a check engine light.
check up on it and let us know.

I don't think 94 had OBD-11

[userpete1037]

94 doesn't have OB-II. I have a 95 and doesn't. OB-II starts at 96 and up. As far as the heater goes, you may want to check the thermostat to see if it's stuck in the open position. I bought my 95 2-years ago and the heater sucked, it didn't warm at all. i changed everything one at a time from thermostat to hoses and water pump only to find out that after all of that, one of my hoses was clogged where it connects into the nipple at the the intake.

[mr_mushroom]

oh wow i thought OBD-I stopped at 92
oops.